1. Field of the Invention
This invention relates to hard disk drives. More specifically, this invention relates to an actuator latch in which the latching mechanism is effectuated by mechanical components.
2. Description of the Prior Art and Related Information
A large market exists for hard disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low cost mass production. In addition, the hard disk drive must provide substantial storage capacity, rapid access to data and reliable performance. Numerous manufacturers compete in this large market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
Each of numerous contemporary mass-market hard disk drive models provides relatively large capacity, often in excess of a few gigabytes per drive. Nevertheless, there exits substantial competitive pressure to develop mass-market hard disk drives that have even higher capacities and that provide rapid access to data at lower prices. Another requirement to be competitive in this market is that the hard disk drive must conform to a selected standard exterior size and shape often referred to as a "form factor." Generally, capacity is desirably increased without increasing the form factor or the form factor is reduced without decreasing capacity.
Satisfying these competing constraints of low-cost, small size, high capacity and rapid access requires innovation in each of numerous components and methods of assembly including methods of assembly of various components into certain subassemblies. Typically, the main subassemblies of a hard disk drive are a head disk assembly ("HDA") and a printed circuit board assembly ("PCBA").
The HDA includes: an enclosure including a base and a cover; at least one disk having at least one recording surface; a spindle motor for causing each disk to rotate; and an actuator arrangement. The printed circuit board assembly includes circuitry for processing signals and controlling operations of the drive.
In a contemporary mass-market disk drive, the actuator arrangement is a type often referred to as a rotary voice coil motor (VCM) actuator. The rotary VCM actuator in a head disk assembly typically includes a permanent magnet arrangement forming part of the voice coil motor, a head stack assembly (HSA), and a pivot bearing cartridge that includes a shaft attached to the base to define an axis of rotation for the rotary actuator. The HSA includes a separate head gimbal assembly (HGA) for each recording surface. The HGA includes transducing structure for writing to and reading from a recording surface of a disk. The transducing structure can be a single inductive transducer such as a thin film head, or a structure including an magnetoresistive (MR) element for reading and an inductive element for writing. The transducing structure is suitably contained in a structure referred to interchangeably as a slider or a head. The HSA further includes a coil-carrying wing or cantilevered portion, the coil of which forms another part of the voice coil motor. The HSA further includes a swing-type structure, and a flex circuit assembly. The swing-type structure has a ring-shaped portion (e.g., a bore extends through it) for surrounding the pivot bearing cartridge, and further includes a plurality of arms cantilevered from the ring-shaped portion.
Each HGA includes a load beam and a slider. Each load beam has a supported end and a free end, with the supported end being supported by one of the arms. Each head is supported by one of the load beams at its free end and is positioned adjacent a disk recording surface when in use.
For each head and recording surface, the relative position of the head and the recording surface involves a vertical distance (such as a flying height or contact) and a radial distance (where the head is relative to the center of the recording surface).
As for vertical distance, while the disks are spinning at normal speed of operation, each head flies adjacent to a recording surface of a disk on a cushion of flowing air. When power is removed and the disks discontinue rotating, the heads "land" on the adjacent surfaces.
As for radial positioning, the HSA forms part of a servo system for controlling the radial position of the heads. The operations of the servo system include track seek operations and track following operations. During a track seek operation, the voice coil motor generates relatively high torque to cause the HSA to rotate about the pivot bearing axis and thereby move the heads radially relative to the disk recording surfaces. During track following operations, the voice coil motor generates relatively low torque in an amount and direction to maintain the heads at substantially the same radial position relative to tracks on the recording surfaces throughout the track following operation.
While the power is off, it is desirable to "park" each head in a position such as on an annular region of the recording surface referred to as a "landing zone." The landing zone is typically located within another annular zone (e.g., the zone used for recording and reading signals which may be further subdivided into zone bands). To park the heads, the HSA is held to prevent it from rotating even if the drive is dropped, struck or otherwise mishandled. To hold the HSA (and thus the heads) in place while the drive is not in use, the HDA typically includes an arrangement that performs a latching function. A related function is a crash stop function. That is, it is desirable to provide an arrangement for limiting the angular motion of the HSA to a range having an inner limit and an outer limit, and for effectively securing or "latching" the HSA while parked.
One such arrangement is illustrated in Prior Art FIG. 1A and FIG. 1B. The illustrated prior art arrangement includes a magnetic actuator latch subassembly 34 and a tang 5. Magnetic actuator latch subassembly 34 includes a dual-post unitary crash stop member 35 having a mounting portion 40 for mounting to a base of a disk drive, a pair of cantilevered, oppositely-projecting arms 36 and 42, and a pair of posts 44 and 48 each supported at a far end of a respective one of the arms 36 and 42. The arrangement also includes a generally cylindrical magnet 46 supported by post 44 in an orientation such that its axis is parallel to the cantilevered arms 36 and 42. Tang 5 is cantilevered to project from a portion of an HSA in a direction such that, in the HDA, the tang 5 is movable between the pair of posts 44 and 48 of the dual-post unitary crash stop member 35.
The tang 5 is generally paddle shaped with first and second oppositely facing surfaces. One of these oppositely facing surfaces abuts post 48 of the dual-post unitary crash stop member 35 to perform the outer crash stop function. The other oppositely-facing surface abuts an end of the cylindrical magnet 46 to perform the inner crash stop and latching functions.
While such an arrangement is useful for its intended purpose, it has certain performance drawbacks. For instance, attractive force of magnet 46 decreases sharply as the separation distance between the magnet 46 and the tang 5 increases when the tang moves out of a latched position. As a result, the cylindrical magnet 46 may accidentally delatch and release the tang 5 when the hard disk drive is dropped, struck or otherwise mishandled.
Such accidental delatching may cause undesirable motions of the head relative to the recording surface of the disk. For instance, the head may crash into the disk (head slap) and cause damage to the disk and the head. Furthermore, debris dislodged from such crashes can cause problems in the operation of the disk drive. In addition, substantial costs are associated with the manufacture of magnetic actuator latch subassembly 34 since the cost of magnet 46 is relatively high compared to the other components of magnetic actuator latch subassembly 34.
Thus, a need exists for an HDA with a low cost actuator latch arrangement that provides for securely holding the HSA in a fixed position when the head is parked and minimizes the risk of accidental delatching.